Electronic spectra of dithieno analogues of phenanthrene

The magnetic circular dichroism (MCD) spectra of some dithieno analogues of phenanthrene: benzo [2,1-b;3,4-b′] dithiophene (I) benzo [1,2-b;4,3-b′] dithiophene (II), benzo [1,2-c;3,4-c′] dithiophene (III) and benzo [1,2-b;3,4-b′] dithiophene (IV) are reported. For I–III the spectra corresponding to two different transition moment directions could be obtained from low-temperature linear dichroism spectra. The results compare well with theoretical energies, oscillator strengths, moment directions and MCD B-terms which were obtained from semi-empirical quantum mechanical calculations in the π-electron approximation.     

Intramolecular azide-diene cycloadditions. An approach to fused bicyclic 3-pyrrolines based on a one-pot nitrene-diene cycloaddition equivalent.

Cyclization of heterosubstituted ω-azidodienes 11 provides fused bicyclic 3-pyrrolines 12 in one operation. These pyrrolines are potentially useful intermediates for natural products synthesis, as illustrated by further functionalization.     

Quasiparticle spectra, charge-density waves, superconductivity, and electron-phonon coupling in 2H-NbSe2

High-resolution photoemission has been used to study the electronic structure of the charge-density wave (CDW) and superconducting dichalcogenide, 2H-NbSe2. From the extracted self-energies, important components of the quasiparticle interactions have been identified. In contrast to previously studied TaSe2, the CDW transition does not affect the electronic properties significantly. The electron-phonon coupling is identified as a dominant contribution to the quasiparticle self-energy and is shown to be very anisotropic (k dependent) and much stronger than in TaSe2.     

X-ray absorption, photoemission spectroscopy, and Raman scattering analysis of amorphous tantalum oxide with a large extent of oxygen nonstoichiometry

The electronic structure and modification of the local interatomic structure of a reactive sputtered amorphous tantalum oxide (a-TaO(x)) thin film with the variation of oxygen nonstoichiometry, x in a-TaO(x) have been investigated by X-ray absorption spectroscopy (XAS), X-ray photoemission spectroscopy (XPS), Raman scattering spectroscopy, and Rutherford back scattering spectroscopy. A parallel chemical shift of Ta4f(7/2) and O1s core levels observed with the variation of x indicates the Fermi level shift by reduction and oxidation in the framework of the rigid band model. Extended X-ray absorption fine structure (EXAFS) suggests both the increase of average coordination number of the first Ta-O shell in polyhedra and a considerable reduction of the average Ta-O bond length with the increase of x. The relative intensity of Raman shift peaks at 670 cm(-1) and 815 cm(-1), corresponding to Ta-O stretching of TaO(6) octahedra and TaO(5) probably with a pyramidal form, respectively, drastically changes between x = 2.47 to 1.86, suggesting the change in the predominant polyhedron from TaO(6) to TaO(5) with a modification in multiplicity of oxygen by the reorganization of the polyhedral network.     

Low energy electronic spectroscopy of an infinite-layer cuprate: A resonant inelastic X-ray scattering study of CaCuO2

We report the results of Oxygen K-edge soft X-ray absorption and emission spectroscopy that was performed on an infinite-layer insulating cuprate thin film CaCuO₂. Experimentally obtained spectra are consistent with local density approximation calculations. X-ray absorption spectra show a close resemblance to spectra obtained from homologous single crystal cuprates. In addition to d–d excitations, X-ray emission spectra reveal the presence of Zhang-Rice singlet states in the infinite-layer CuO₂ planes. The question of whether the Zhang-Rice singlet features are masked by the O 2p main-band is addressed: it is possible to quantify the position of the Zhang-Rice singlet using emission intensity profiles. X-ray emission is demonstrated as a tool for understanding CuO₂ planar electronic correlation in the prototypical infinite-layer. The energy difference, 2.0 eV, between the oxygen main-band and the Zhang-Rice singlet band is found to match values obtained theoretically using established planar electronic correlation parameters.     

An Advanced Materials Beamline for Energy Research (AMBER)

Detailed mapping of the electronic structure is a crucial part of explaining the behavior of materials. It is the electronic structure that determines the conductivity and thermal properties. It is the electronic structure that determines chemical properties. Knowledge about the electronic structure can help in determining the atomic structure of molecules.     

ESI-MS detection of proposed reaction intermediates in the air-promoted and ligand-modulated oxidative Heck reaction

Electrospray ionization mass spectrometry (ESI-MS) and subsequent MS/MS analyses were used to directly detect palladium-containing cationic reaction intermediates in a ligand controlled palladium(II)-catalyzed oxidative Heck arylation. All potential intermediates were observed as dmphen-ligated palladium(II) species, suggesting that the dmphen bidentate ligand is attached to the metal center during the entire catalytic cycle. The study supports previous mechanistic propositions and provides new information regarding the composition of aryl-containing Pd(II) complexes in an ongoing oxidative Heck reaction. In addition, sodium acetate was found to be a useful base alternative to previously used tertiary amines.     

Synthesis and polymerization of (E,E)-[6.2](9,10)anthracenophane-1,5-diene

The title compound has been synthesized by dimerization of a substituted p-xylylene, generated via a 1,8-Hofmann elimination. Several unique isomers of this dimer are also obtained. The title diene can be polymerized cationically to give low molecular weight polymer. Oxidative doping of this polymer with iodine forms a material with a conductivity of 3 × 10^?4 S/cm. In contrast to previously reported anthracenophanes this polymer is photochemically unreactive.